The present invention relates to an improved roofing composition which is useful both for re-roofing existing installations and also in the construction of new roofing. More particularly, the invention is concerned with a roofing composition which is superior to asphalt and known asphalt compositions modified with synthetic resins.
Asphalt is a common material utilized in the production of roofing coatings. Deficiencies in some physical properties of asphalt may be improved by admixing various resins, rubbers, fillers and other modifiers therewith.
When an entire surface is to be re-roofed, requirements for a suitable roofing composition are more stringent than those for new roofing. The surface to which new roofing is applied can be carefully controlled and virtually as dust, dirt and sediment free as possible. This is not true of old roofing to which a re-roofing membrane is to be applied. A coating system is usually formulated to protect and to add years of service to existing conventional-type roofing. A re-roofing membrane must be designed to tie in with existing roofing and to fill voids without requiring an extensive effort to prepare the surface to which the roofing composition is applied.
Faulty existing roofing cannot be conveniently washed without introducing water through weak portions thereof. Moreover, it is difficult to dry such washed roofing since water tends to penetrate weak spots. After applying a new coating to washed faulty roofing, any non-removed moisture can impair the effectiveness of the coating applied thereover.
It is known to produce a roofing utilizing felts and hot asphalt or tar in alternate layers or utilizing base felts mopped in with asphalt or tar. A protective layer of gravel or crushed slate or the like may be applied to the top of the upper bituminous layer to improve the weathering properties of the roofing and to change the color of the roofing from the black color of asphalt.
One known approach to modifying asphalt by the addition of synthetic resins is disclosed in U.S. Pat. No. 3,345,316 to Nielsen. This patent discloses asphalt compositions stated to be suitable for roofing purposes as well as for special binders. The composition of this patent is said to contain three essential components:
(a) 45-75% by weight of an asphalt of the group consisting of straight run asphalt having a viscosity between about 350-450 SSF at 210.degree. F., blown asphalt having a softening point between about 110.degree. F. and 185.degree. F., and mixtures thereof;
(b) 15-35% by weight of chlorinated polyphenyl resins containing from about 30% to about 65% by weight of chlorine;
(c) and 10-30% by weight of a block copolymer of the group consisting of copolymers having the general configuration EQU A-B-A
wherein each of A is a polymer block of a vinyl arene and B is a polymer block of a conjugated diene; the average molecular weight of A being between about 8,000 and 45,000, the average molecular weight of B being between about 40,000 and 125,000, the total A content of the block copolymer being between about 23 and 40 weight percent; and hydrogenated derivatives of such block copolymers.
Muir (U.S. Pat. No. 3,755,231) concerns process-equipment-coating compositions containing terminally-reactive diolefin polymer, curing agent for that polymer, a bituminuous substance, an A(BA).sub.n block copolymer, solvent for the latter and, optionally, a reinforcing filler, such as carbon black or silica. In the block copolymer A can be polystyrene, and B may be an ethylene-propylene copolymer.
Holden (U.S. Pat. No. 3,265,765) provides elastomeric block polymers A-B-A which may be dispersed in asphalt to improve hot temperature viscosity and low temperature ductility and flexibility (column 7, lines 36 and 38). The elastomers may be mixed with the usual rubber compounding materials, such as carbon blacks (column 7, lines 44 and 45). In these block polymers each A can be an alkenyl aromatic hydrocarbon connected by a block of a polymerized conjugated diene (column 2, lines 39 to 46).
Problems with currently-employed re-roofing compositions and factors which contribute to these problems are readily appreciated by considering literature provided on one such composition. In the remainder of the BACKGROUND only the bracketed text is commentary; the rest is from the noted literature.
Probably the most important problem to consider when reroofing becomes a necessity is . . . Should we reroof with the same product that has failed? Asphalt and coal tar, popular roofing of the past, are subject to deterioration from sunlight, water, and movement . . . the very elements they should be providing protection from. With [this roofing system] you can make your building watertight without removing the existing roof. . . .
[This roofing system] is a one-part moisture cured urethane system that is compatible with asphalt and coal tar.
This system which has excellent adhesive properties to most surfaces . . .
is flexible . . . will stretch and move as the roof moves. PA1 is watertight . . . forms a continuous envelope over a roof surface. PA1 is less costly than replacing old roofing . . . with proper surface preparation can be applied directly over old roofing.